It has become desirable in various industries to have hydraulic cylinders that move in synchronization with each other, whether it is a retracting motion or an extending motion or both. One device used to synchronize the movement of multiple hydraulic mechanism cylinders is called a series cylinder or synchronizing cylinder. Synchronizing cylinders are generally described in U.S. Pat. Nos. 4,409,884 (Boehringer) and 6,408,736 (Holt et. al.), which are hereby incorporated by reference. Generally, a synchronizing cylinder is a cylinder in a hydraulic circuit that aids in delivering a predetermined volume of fluid to several mechanism cylinders at the same time. (The mechanism cylinders are the cylinders that combine with the mechanism that is being moved by the hydraulic power.) The synchronizing cylinder is actually several cylinders tied together in one unit. There is one chamber in the synchronizing cylinder for each mechanism cylinder. There is a piston in each synchronizing cylinder chamber to move the fluid. The pistons are tied together by a rod so that when one piston moves, the other piston(s) moves the same distance at the same speed.
Traditional synchronizing cylinders generally perform well, however, they comprise elements that make them complex and expensive to manufacture. FIG. 9 shows a sectional view of a traditional synchronizing cylinder 110 comprising some of the elements that make traditional synchronizing cylinders 110 complex and expensive. FIG. 9 shows a synchronizing cylinder 110 having a hollow rod 80, a seal 84, and an external rod portion 82. Traditional synchronizing cylinders 110 require the hollow rod 80 to connect the cap sides of the chambers for synchronizing purposes. The seal 84 is a fluid barrier between the cap side of one chamber and the rod side of the adjacent chamber. The seal 84 has been required in traditional synchronizing cylinders 110 to direct the proper volume of fluid to and from the respective chambers of the synchronizing cylinder 110. The external rod portion 82 is a portion of the rod 120 that extends out from the cylinder 110 as the cylinder 110 is retracted. The external rod portion 82 has been required in traditional synchronizing cylinders 110 to ensure that the volume of each chamber was equal. Without the external rod portion 82 moving into the synchronizing cylinder 110 as the cylinder 110 is extended, the end chamber would have a volume greater than the other chambers in the synchronizing cylinder 110.